Gas bag systems where a cushion is automatically inflated in front of the occupant by means of a gas generator in the event of a crash are known both for the driver seat and also for the passenger seat.
In order to ensure safe protection of the occupant in the event of a vehicle crash, the gas bag has to be inflated within a short time. In practice, the inflation takes place within few milliseconds. It is thereby ensured that the gas bag is already inflated in the event of an accident before the occupant is slung towards the gas bag. It is thereby assumed that the occupant is located in a normal position predetermined by the seat so that the occupant does not impact the gas bag during inflation.
However, this case does not exist if the occupant has bent forward during vehicle impact with his head in the region of inflation for the gas bag. Then the gas bag inflated in the aforementioned short time strikes against the occupant which may injure the passenger.
In order to overcome this drawback, German Patent No. 42 27 559 discloses inflating the gas bag in the direction of the occupant (axial direction) with a comparatively slow speed, and in the sideways direction with a comparatively quick expansion speed. This device has the drawback however that if the occupant is flung forwards in the event of impact, the gas bag is still not fully inflated in the axial direction which lessens the effectiveness of the gas bag in preventing injury.
Although on the one hand it is desirable to avoid the occupant impacting the gas bag as it inflates, it is also desirable that the occupant impacts the gas bag as early as possible after its full inflation if the occupant is still located in the normal position during impact. This is not guaranteed, particularly in the case of a passenger gas bag, since the gas bag inflates in directions other than in the driver direction. The disadvantages here are that the distance between the inflated gas bag and the occupant is relatively large and that the surface of the gas bag with which the occupant comes into contact is reduced. The surface pressure on the occupant is thereby unfavorably large.
This drawback is avoided with an airbag module described in U.S. Pat. No. 5,306,042. A rotatable and displacable cover flap is provided between the gas generator and the windshield and is closed in the direction of the windshield but is open in the direction of the gas generator and vehicle occupant. The gas emerging from the gas generator first flows towards the cover flap, pressing it up to a stop position so that the deployment of the gas bag is directed toward the occupant.
The drawback with this cover flap is that it is considerably more expensive compared with other more conventional cover flaps which are formed as an integrated component part of the panel lining.
A further known possibility for influencing the expansion direction is in the use of arrester straps as described in European Patent No. 0 593 010 Al. However, sewing in arrester straps is likewise expensive.
It is therefore desirable to provide an airbag module which, in the event of impact by the vehicle, allows early contact between the gas bag and occupant with reduced surface pressure on the occupant, and without the need for more expensive designs of known airbag modules.